1. Field of the Invention
The present invention relates to steam valves, for example, for power-generating facilities, and specifically, to a steam valve that is provided with an improved valve body to ensure and maintain a steady flow of steam passing through a gap between the valve body and a valve seat.
2. Related Art
Generally, steam turbines used in power-generating facilities, such as thermal power plants and nuclear power plants, are provided with many steam valves for controlling the amount of steam flow according to load changes, or for cutting off the supply of steam in response to an emergency.
A steam control valve, among steam valves used in thermal power plants and the like, deals with a large amount of hot and high-pressure steam flow and, therefore, frequently opens and closes its valve body. This causes steam to drift or swirl in the beginning process of opening the valve body or in the process of closing the valve body. Such steam turbulence results in noise, vibration, erosion, and accidents, such as cracks in a connecting part of a valve rod supporting the valve body.
A number of inventions have been provided to prevent such problems and accidents, such as disclosed in, for example, documents or publications of Japanese Unexamined Patent Publications Nos. SHO 56-109955, HEI 9-72430, HEI 9-210244, HEI 10-89494, HEI 10-299909, and HEI 10-299910.
In particular, Japanese Unexamined Patent Publication No. SHO 56-109955 discloses a so-called pioneering technique that was developed when noise and vibration were serious issues.
In recent power-generating facilities planning to introduce ultra-supercritical pressure technology, steam conditions (temperature and pressure) increase as the single capacity of a steam turbine increases. Such increases in steam conditions cause noise and vibration to be a major concern again.
To reduce noise and vibration, techniques that are the results of development and are disclosed in the above-described documents have been conventionally used in dealing with subcritical pressure at a pressure of 169 ata and a temperature of 538° C., and supercritical pressure at a pressure of 246 ata and a temperature of 538° C. However, initiatives to introduce ultra-supercritical pressure technology require new techniques to be developed and cause the above-described conventional techniques to reach their limits.
In particular, a common challenge for turbine producers to further reduce noise and vibration is to determine the size of the edge of the valve body such that a steady steam flow can be ensured and maintained even if the above-described steam conditions increase further.